"About 90 percent of cancer deaths are related to metastases, but now we've found a way to dispatch an army of killer white blood cells that cause apoptosis - the cancer cell's own death - obliterating them from the bloodstream.

"When surrounded by these guys, it becomes nearly impossible for the cancer cell to escape."

In laboratory tests Prof King injected human blood samples, and later mice, with two proteins, one which acts as an adhesive and one which kills cancer cells.

When a cancer cell comes into contact with sticky proteins, which is nearly unavoidable in the frenzied flow of blood, the cancer cell essentially kills itself.

He added: "The mechanism is surprising and unexpected in that this repurposing of white blood cells in flowing blood is more effective than directly targeting the cancer cells with liposomes or soluble protein."

When treating cancer cells with the proteins in saline, the researchers found a 60 per cent success rate in killing the cancer cells.

In normal laboratory conditions, the saline lacks white blood cells to serve as a carrier for the adhesive and killer proteins.

Once the proteins were added to flowing blood that mimicked human-body conditions, however, the success rate in killing the cancer cells jumped to nearly 100 percent.

Dr Sarah Hazell, senior science information officer at Cancer Research UK, said: “This new approach is a very exciting piece of science that may hold great promise in its ability to stop cancer cells spreading.

It’s early days at the moment though, because the research was done in human blood in the lab and in live mice, but not in patients.

"Much more research is needed to see if the technique could actually stop the spread of cancer in humans.”

The study was published online in the journal Proceedings of the National Academy of Sciences.